1. Field of the Invention
The present invention relates to a composition to form an overcoat layer for an organic photoreceptor and an organic photoreceptor employing an overcoat layer prepared from the composition. More particularly, the invention relates to a composition forming an overcoat layer constituting an outermost layer of an organic photoreceptor used to form an electrophotographic image, and an organic photoreceptor having good electrical and mechanical properties and improved adhesion of the overcoat layer by employing the overcoat layer prepared from the composition.
2. Description of the Related Art
In electrophotography, an organic photoreceptor includes a photosensitive layer formed on a conductive base and is in the form of a plate, disk, sheet, belt, or drum.
The principles of electrophotographically forming an image will be described briefly below. First, the surface of the organic photoreceptor is electrostatically uniformly charged and irradiated with a laser beam. Positive and negative charges are generated in portions into which a laser beam is irradiated and migrate to the surface. As the surface charges are neutralized, the surface potential in an exposed area is changed so that a latent image is formed.
Thereafter, when the latent image is developed with a toner, a visible image is formed on the surface of the organic photoreceptor. The formed image is transferred to the surface of a receiver, such as paper. The imaging process is repeated.
Both single layer and multilayer photoconductive elements have been used. In the single layer embodiment, a charge transport material and a charge generating material are combined with a polymeric binder, and then are coated on the conductive base. In the multilayer embodiment, the charge transport material and charge generating material are in the form of separate layers, each of which can optionally be combined with a polymeric binder, and then coated on the conductive base. Two arrangements are possible. In one arrangement (the “dual layer” arrangement), the charge generating layer is coated on the conductive base, and the charge transport layer is coated on top of the charge generating layer. In an alternate arrangement (the “inverted dual layer” arrangement), the order of the charge transport layer and charge generating layer is reversed.
In both the single and multilayer photoconductive elements, the purpose of the charge generating material is to generate charge carriers (i.e., holes and electrons) upon exposure to light. The purpose of the charge transport material is to accept these charge carriers and transport them through the charge transport layer in order to discharge a surface charge on the photoconductive element.
In general, the photoreceptor easily wears due to friction against a toner, a roller or a cleaning blade during an imaging process, so that the thickness thereof decreases, and the life thereof is shortened. For this reason, an overcoat layer is coated on the organic photoreceptor.
In manufacturing the overcoat layer of the organic photoreceptor, the use of silsesquioxane-based silicon hard-coat materials is disclosed in U.S. Pat. Nos. 6,187,491 and 5,731,117.
The silicon hard-coat materials have good wear resistance and may easily introduce chemical functional groups and adjust mechanical and electrical properties. Also, since alcoholic solvents used in forming an overcoat layer do not adversely affect a general organic photoreceptor, they are widely used as overcoat forming materials.
However, since such a silicon hard-coat material has weak adhesion to a photoreceptor so that it is easily peeled off or worn, it is necessary to form an adhesive layer or primer layer thereon.
Such an additional step of forming the adhesive layer results in an increase in cost. Also, electrical characteristics of an organic photoreceptor, such as exposure potential or residual potential, are degraded.